P0051
2GR-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0031,P0032,P0051,P0052: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
DTC P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
DTC P0032 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)
DTC P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)
DTC P0052 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)
CAUTION / NOTICE / HINT
HINT:
- Although the DTC titles say the oxygen sensor, these DTCs relate to the air fuel ratio sensor.
- Sensor 1 refers to the sensor mounted in front of the three-way catalytic converter and located near the engine assembly.
DESCRIPTION
The air fuel ratio sensor generates a voltage* that corresponds to the actual air fuel ratio. This sensor voltage is used to provide the ECM with feedback so that it can control the air fuel ratio. The ECM determines the deviation from the stoichiometric air fuel ratio level, and regulates the fuel injection time. If the air fuel ratio sensor malfunctions, the ECM is unable to control the air fuel ratio accurately.
The air fuel ratio sensor is the planar type and is integrated with the heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows into the heater to heat the sensor, in order to facilitate accurate oxygen concentration detection. In addition, the sensor and heater portions are narrower than the conventional type. The heat generated by the heater is conducted to the solid electrolyte through the alumina, therefore the sensor activation is accelerated.
A three-way catalytic converter is used in order to convert the carbon monoxide (CO), hydrocarbon, and nitrogen oxides (HOx) into less harmful substances. To allow the three-way catalytic converter to function effectively, it is necessary to keep the air fuel ratio of the engine near the stoichiometric air fuel ratio.
*: Value changes inside the ECM. Since the air fuel ratio sensor is the current output element, a current is converted to a voltage inside the ECM. Any measurements taken at the air fuel ratio sensor or ECM connectors will show a constant voltage.
HINT:
- When any of these DTCs are set, check the air fuel ratio sensor voltage output by selecting the following menu items on the Techstream: Powertrain / Engine and ECT / Data List / A/F Control System / AFS Voltage B1 S1 or AFS Voltage B2 S1.
- Short-term fuel trim values can also be read using the Techstream.
- The ECM regulates the voltages at the A1A+, A2A+, A1A- and A2A- terminals of the ECM to a constant level. Therefore, the air fuel ratio sensor voltage output cannot be confirmed without using the Techstream.
- If an air fuel ratio sensor malfunction is detected, the ECM sets a DTC.
HINT:
- When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the air fuel ratio sensor heater in fail-safe mode. Fail-safe mode continues until the ignition switch is turned off.
- The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The air fuel ratio sensor heater circuit uses a relay on the +B side of the circuit.
HINT:
- Bank 1 refers to the bank that includes cylinder No. 1.
- Bank 2 refers to the bank that does not include cylinder No. 1.
- Sensor 1 refers to the closest sensor to the engine assembly.
- Sensor 2 refers to the furthest sensor away from the engine assembly.
MONITOR DESCRIPTION
The ECM uses information from the air fuel ratio sensor to regulate the air-fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the three-way catalytic converter to purify the exhaust gas.
The air fuel ratio sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element.
The zirconia element generates small voltage when there is a large difference in the oxygen concentrations between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.
The air fuel ratio sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty-cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the air fuel ratio sensor will be inaccurate, as a result, the ECM will be unable to regulate air-fuel ratio properly.
When the current in the air fuel ratio sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and sets a DTC.
Example:
- The ECM sets DTC P0032 or P0052 when the current in the air fuel ratio sensor heater is fail. Conversely, when the heater current is less than 0.8 A, DTC P0031 or P0051 is set.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
P0031 and P0051:
P0032 and P0052:
TYPICAL MALFUNCTION THRESHOLDS
P0031 and P0051:
P0032 and P0052:
COMPONENT OPERATING RANGE
MONITOR RESULT
Refer to CHECKING MONITOR STATUS Mode 6 Data.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT: Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
PROCEDURE
1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the air fuel ratio sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
Bank 1
Bank 2
(c) Reconnect the air fuel ratio sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)
(a) Disconnect the air fuel ratio sensor connector.
(b) Turn the ignition switch on (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:
Bank 1
Bank 2
(d) Reconnect the air fuel ratio sensor connector.
NG -- INSPECT FUSE (A/F FUSE)
OK -- Continue to next step.
3. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR RELAY - ECM)
(a) Disconnect the air fuel ratio sensor connector.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Bank 1
Bank 2
Standard resistance (Check for short):
Bank 1
Bank 2
(d) Reconnect the ECM connector.
(e) Reconnect the air fuel ratio sensor connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - ECM)
OK -- Continue to next step.
4. CHECK WHETHER DTC OUTPUT RECURS
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch on (IG).
(c) Turn the tester on.
(d) Clear the DTCs DTC Check / Clear.
(e) Start the engine.
(f) Allow the engine to idle for 1 minute or more.
(g) Select the following menu items: Powertrain / Engine and ECT / Trouble Code.
(h) Read the DTCs.
Result:
B -- REPLACE ECM
A -- CHECK FOR INTERMITTENT PROBLEMS
5. INSPECT FUSE (A/F FUSE)
(a) Remove the A/F fuse from the engine room relay block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reinstall the A/F fuse.
NG -- REPLACE FUSE (A/F FUSE)
OK -- Continue to next step.
6. INSPECT ENGINE ROOM JUNCTION BLOCK ASSEMBLY (A/F RELAY)
(a) Inspect the A/F relay Testing and Inspection.
NG -- REPLACE ENGINE ROOM JUNCTION BLOCK ASSEMBLY
OK -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F FUSE - AIR FUEL RATIO SENSOR)